This is a prospective, baseline-controlled open label study in patients with NYHA Class II-IV CHF who are currently receiving beta-blocker therapy with carvedilol or metoprolol. The objective of this study is to investigate the efficacy and safety of intravenous milrinone when administered to patients with congestive heart failure who are being treated with long-term (> 3 months) beta-blocker therapy with carvedilol or metoprolol. This study will also serve as a pilot study to help determine the appropriate dosing of intravenous milrinone for a planned comparative study to dobutamine.